Methods of forming microstructure devices

Details Methods of forming microstructure devices Methods of forming microstructure devices

2001-05-07

2003-06-10

Coloman, William David (Department: 2823)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Physical stress responsive

C438S477000, C438S706000, C216S002000

Reexamination Certificate

active

06576489

ABSTRACT:

TECHNICAL FIELD
The invention pertains to methods of forming microstructure devices, such as, for example, methods of forming microelectromechanical systems (MEMS).
BACKGROUND OF THE INVENTION
There are numerous applications developed, and being developed, for microstructures, such as, for example, microelectromechanical systems (MEMS). The microstructures are commonly fabricated from semiconductive materials, such as, for example, silicon. Frequently, a microstructure will include a pair of components which are spaced from one another, and which move relative to one another during operation of the microstructure. Ideally, the components can be repeatedly moved together and apart. However, a problem that can occur in forming and using microstructures is that semiconductive materials formed into MEMS can irreversibly adhere to one another as they are moved toward one another or during the fabrication process. Such problem can be manifested as an inability to release the materials, and the release-related problem is typically referred to in the art as “stiction”.
An exemplary prior art fabrication process for forming a microstructure device is described with reference to
FIGS. 1-3
. Referring initially to
FIG. 1
, a portion of a prior art semiconductive assembly
10
is shown in fragmentary view at a step occurring during a micromachining process. Assembly
10
comprises a first semiconductive material
12
, a sacrificial layer
14
over material
12
, and a second semiconductive material
16
over sacrificial layer
14
. Semiconductive material
12
can comprise, for example, a single-crystal silicon wafer, or can comprise silicon in a polycrystalline or amorphous form. Sacrificial layer
14
can comprise, for example, silicon dioxide or organic films; and second semiconductive material
16
can comprise, for example, polycrystalline or amorphous silicon. Material
12
can be referred to as a semiconductive material substrate, or alternatively a combination of materials
12
and
14
can be referred to as a semiconductive material substrate. To aid in interpretation of this disclosure and the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
It is to be understood that the above described materials
12
,
14
and
16
are exemplary materials, and that other materials can be utilized. For instance, material
16
will sometimes comprise silicon nitride, and sacrificial material
14
will sometimes be silicon.
Referring next to
FIG. 2
, sacrificial layer
14
(
FIG. 1
) is removed to leave a first gap
20
between a portion of first semiconductive material
12
and second semiconductive material
16
, and a second gap
22
between another portion of first semiconductive material
12
and second semiconductive material
16
. Second semiconductive material
16
defines a beam supported by first semiconductive material
12
. If sacrificial material
14
comprises silicon dioxide, such can be removed utilizing a hydrofluoric acid etch.
Referring next to
FIG. 3
, a stiction problem is illustrated. Specifically, a portion of second semiconductive material
16
has moved relative to first semiconductive material
12
and is non-releasably adhered to the first semiconductive material. The movement of second semiconductive material
16
relative to first semiconductive material
12
can occur either during operation of a device comprising assembly
10
, or during removal of sacrificial layer
14
. If the stiction occurs concomitantly with removal of sacrificial layer
14
(
FIG. 1
) it is referred to as “release-related stiction”, and if it occurs after removal of sacrificial layer
14
, (for example, during utilization or shipping of a microstructure comprising assembly
10
), it is referred to as “in-use stiction.”
It has been recognized that one way to alleviate the release-related stiction is to use supercritical CO
2
drying. Also, it has been recognized that one way to alleviate in-use stiction is to form a self-assembled monolayer (SAM) coating across semiconductive material surfaces to alleviate binding of the surfaces to one another. An exemplary SAM coating can be formed by exposing a semiconductive material surface to an alkyltrichlorosilane (RSiCl
3
), such as, for example, octadecyltrichlorosilane [CH
3
(CH
2
)
17
SiCl
3
; OTS] or 1H, 1H,2H,2H-perfluorodecyltrichlorosilane [CF
3
(CF
2
)
7
(CH
2
)
2
SiCl
3
; FDTS]. Alternatively, an exemplary SAM coating can be formed by exposing a semiconductive material surface to a dialkyldichlorosilane (R
2
SiCl
2
).
For purposes of interpreting this disclosure and the claims that follow, semiconductive materials
16
and
12
are referred to as being moved relative to one another if either of components
12
and
16
comprises a portion which moves relative to a portion of the other of the components. In particular applications, both of components
12
and
16
can be moved when the components are moved relative to one another.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a method of forming a microstructure device. A substrate is provided within a reaction chamber. The substrate has a first surface spaced from a second surface, and is ultimately to be incorporated into the microstructure device. The first and second surfaces are ultimately to be movable relative to one another in the microstructure device. Alkylsilane-containing molecules are introduced into the reaction chamber in a vapor phase, and at least one of the first and second surfaces is exposed to the alkylsilane-containing molecules to form a coating on the at least one of the first and second surfaces.
In another aspect, the invention encompasses another method of forming a microstructure device. A substrate is provided which has a first semiconductive material surface separated from a second semiconductive material surface by a gap. At least one of the first and second semiconductive material surfaces is exposed to OH radicals. After the exposure to the OH radicals, the at least one of the first and second semiconductive material surfaces is exposed to vapor-phase alkylsilane-containing molecules to form a coating over the at least one of the first and second semiconductive material surfaces.
In yet another aspect, the invention encompasses another method of forming a microstructure device. A substrate is provided which has a first semiconductive material, a second semiconductive material, and a sacrificial material between the first and second semiconductive materials. The substrate is exposed to vapor-phase etchant to remove at least some of the sacrificial material from between the first and second semiconductive materials, and subsequently at least one of the first and second semiconductive materials is exposed to vapor-phase alkylsilane-containing molecules to form a coating over the at least one of the first and second semiconductive materials. The method can be utilized to solve both release-related and in-use stiction problems.


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“Plasma enhanced chemical vapor deposition of fluorocarbon thin film via CF3H/H2chemistries: Power, pressure and feed stock composition” Jay J. Sankevich and David E. Sherrer II; J. Vac. Sci. Technol. A18(2) Mar./Apr.

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